Integrated circuits ("IC") are the tiny "chips," usually less than 0.5" on a side, of silicon (or other similar material) on which is patterned the transistors and interconnections that make modem electronic systems do what they do; compute, amplify, etc. Many advances in IC fabrication processes have brought about dramatic increases in the number of transistors that can be fabricated on each chip, thereby increasing the capabilities, as well as decreasing the size of ICs and, thus, the size of devices using ICs. Whereas the actual size of a typical IC is much less than the size of a conventional IC package, novel IC packaging designs that can significantly reduce the size of electronic devices are being explored. Moreover, as ICs become faster and more powerful, device packaging becomes a major limitation on system speed.
Conventional IC packages consist of the same basic elements: the IC, a lead frame, wire bonds, and an encapsulant. The lead frame is connected to the IC using a very thin wire bonded to both the chip and the lead frame. The encapsulant or molding, usually made from plastic, forms a package that encloses the IC, wire bonds, and part of the lead frame, thereby protecting the IC from the ambient environment. An electronic system is typically constructed from multiple packaged IC devices, which are electrically- and physically-coupled to a printing circuit board ("PCB") by leads that form a portion of the lead frame and which extend from the IC package; the PCB including metallic traces for interconnecting the multiple ICs. A relatively new approach to packaging is to place more than one IC in the same package; the multiple IC package is called a Multi-Chip Module ("MCM"), or a "hybrid" package.
MCM packages are similar to conventional single-chip package designs. MCM packages, however, house more than one IC by mounting conventional chips on a common substrate, which has metallic paths formed thereon that interconnect the individual chips. A conventional lead frame is connected to terminals on the substrate using a very thin wire, and the substrate and lead frame are then enclosed by an encapsulant to form a protective package.
The current objective in electronic systems is toward smaller, lighter, faster, portable systems; e.g, cellular telephones, pagers, notebook computers. The development of MCMs may play an important role in furthering that objective by eliminating a level of packaging for many components, facilitating the integration of multiple analog and digital technologies in a single module, reducing electromagnetic interference ("EMI") problems, and increasing the input/output ("I/O") capabilities per chip. Furthermore, chip-to-chip wiring within a MCM is cheaper and faster than PCB wiring and reduces the board area needed for a device.
In some cases, the capabilities of ICs designed for conventional single chip packages is reduced due to a desire to reduce the package size, which necessarily requires reducing the number of package leads. For example, although an IC may process data internally using a plural-conductor (i.e., "parallel") bus, the data may be serialized such that it can be communicated to another IC through only one lead. In an MCM, however, there are no leads associated with individual ICs; i.e., the ICs are coupled internally via very small metallic paths formed on a common substrate that is coupled to a lead frame. Thus, although a principle advantage of MCMs is the capability to integrate many ICs in one package, that advantage is partially diminished if it is necessary to design ICs specifically for use in MCMs, rather than using ICs designed for conventional single-chip packages.
Therefore, what is needed in the art are circuits and methods for employing conventional ICs in MCMs. There is a further need in the art for techniques of integrating conventional ICs in MCMs such that the performance of the conventional ICs is enhanced when employed in an MCM.